Shipping has experienced considerable structural changes in recent years. Particularly in container shipping, ship sizes, layover days, loading strategies and hence the amount of ballast water, the residence times thereof and the mixing ratios thereof in harbour and coastal areas have changed considerably resulting in new scenarios and consequently new risks for the transfer of exotic species and bacteria which are pathogenic for humans. Particularly in recent years, it has been confirmed on the basis of extreme examples that such organisms are being transferred with the ballast water from ships to other places with far-reaching consequences for ecology and health. One example of this is the appearance of the zebra mussel in the Great Lakes of North America. This has led both to an alteration in the food structure with consequences for fishing and tourism and to a burden on the energy industry due to the high costs of combating the mussels in power station cooling circuits. Lasting and in some cases irreparable long-term damage is also being caused by the massive transfer of resting cysts of toxic algae which not only results in unwanted bloom but also endangers the cultivation of mussels and oysters in many coastal regions. Finally, the transfer of a species akin to the jellyfish to the Black Sea a few years ago led to the complete collapse of sardine fishing.
The intercontinental transfer of infectious bacteria which are pathological for humans, such as Vibrio Cholearae, serotype 01 L, has been proven by the Institute for Molecular Biology, Baltimore, USA. These examples demonstrate that there is an urgent need for action to develop measures for reducing the risk of transferring exotic plant and animal organisms and pathological bacteria with the ballast water of ships.
There have been many attempts to develop suitable methods for treating ballast water of ships. These methods did not become established because of insufficient effectiveness and/or shortcomings. Although microorganisms can be destroyed by treating the water with strong UV radiation, such radiation does not kill larger organisms contained in zooplankton such as Artemia, crabs, mussels and the eggs thereof. Moreover, UV technology also necessitates expensive pumping of the ballast water.
Ozone is an effective biocide but ozonation of the ballast water of ships is technically too complex. Treatment of the ballast water with hypochlorite has the disadvantages of the formation of organochlorine compounds, the poor stability of hypochlorite, and the corrosiveness thereof.
Many organic compounds are known which are highly effective biocides but their long-term effect or their high stability make them undesirable for use in ballast water. After treatment it should be possible to discharge the biocides with the ballast water in a largely degraded and ecologically harmless form into the aquatic environment. The transit times of a ship and hence the treatment time of the ballast water may range from a few days to many weeks, so control of the residual biocide content is no longer guaranteed.
It is well known that hydrogen peroxide, which decomposes to water and oxygen, has a biocidal effect on certain microorganisms, but mostly only a biostatic effect. The oxidation potential of hydrogen peroxide is generally too low to damage organisms of the zooplankton effectively or to kill them. A process for preventing contamination of navigable waters by cysts of harmful plankton is described in U.S. Pat. No. 5,256,423, which process consists of adding an effective amount of hydrogen peroxide to the ballast water and discharging the ballast water only after a sufficiently long reaction time during which the cysts are substantially destroyed. The cysts which can be destroyed by this process are resting stages of the algae belonging to the phytoplankton. As practical experience has shown, the spectrum of action of hydrogen peroxide is not sufficient for treating ballast water because other stages and types of phytoplankton and zooplankton, including their resting stages which are also present in the ballast water, are destroyed incompletely, if at all.
It is known from U.S. Pat. No. 5,393,781 that zebra mussels in the adult and larval forms can be controlled by contact with peracetic acid. A solution containing peracetic acid in an effective amount is added, for example, to a water inlet or a storage vessel of a water treatment plant. The use of a peracetic acid solution for the treatment of ballast water of ships in order to prevent the transfer of species of organism to a new locality or from one aquatic environment to another is neither disclosed nor suggested in this document. Furthermore, it does not disclose whether and on what scale the eggs of zebra mussels and of other organisms of the zooplankton including the epifauna thereof are destroyed by peracetic acid.